The desirability of achieving maximum bonding strength between urethane formulations and cured rubber or synthetic rubber substrates has long been known in the art. The bonding of urethane formulations to cured rubber or synthetic rubber substrates has been one of the more difficult problems experienced in the rubber industry and also with users of rubber products. The conventional use of adhesives, primers, bonding agents, etc., available commercially has been unable to provide a urethane-to-rubber bond that is equal in pull strength to a rubber-to rubber bond.
Laboratory adhesion tests using conventional methods of applying primers or adhesive agents, such as cyanoacrylates, allowing them to dry and then applying a urethane formulation as a liquid or a paste and allowing it to cure, normally produces a bond strength ranging from 1 to 30 pli (pounds per linear inch). A desirable bond strength should be at least 80 pli.